I can not unlock my log in user name

Hi,

I was trying to change my login name, first I unlocked the lock icon at the bottom of the "users & groups " window, then I right clicked on the admin, then clicked on advance option, then changed the name, then restarted my Mac, then login name was still the same as before, I then went into the users & group window again and I realised that the status of my login changed from admin to standard, now I can not even unlock it anymore. when I click on the lock icon, it shows a window with empty user name, and no matter what I enter into it, nothing happens. I have search through internet and the apple community but no suggestion worked for me. I have tried the command +R went to utilise\terminal\resetpassword to change the password but still not able to unlock the user&group window. Please help if anyone knows how to fix this. Thank you!